Bruce In Philly

The hesitation, dropout, has been the exact same for 90 k miles on my 2009 C2S.

I keep threatening to change out my actuators on my next plug change in desperation, but I learned that the computer throws a code if they hiccup... and I have no engine codes in 90k miles (i have a Durametric) So... I dunno....

Peace
Bruce in Philly

lowbee

So I had my water pump replaced, a new drivebelt kit and LN low temp thermostat installed. In the process a lot of the stuff (airbox, pulleys, drivebelt, etc) have to come off and be re-installed. And....what do you know ..... the phazzzz sounds whenever I ease into the throttle at 2700 rpm is 90% gone..... I don't know which part that got re-installed helped this but I like the end result.... thought I share.

And88

Had it on my 09 C2S 6MT, do not have it on my 2011 C2 PDK.

lowbee

A little off topic but do you enjoy your PDK as much as the 6MT ? or does the thought of wishing your 2011 C2 was a 6MT ever crossed your mind ?

And88

Thats a great question- and no, I don't miss it. not in my current situation. I got into the pdk cause I was miserable commuting 45 miles each day in LA traffic with a manual transmission. I felt awful for the car; it really
seemed to hate traffic and the rare times I could open it up on the weekends didn't make it worth it for me.

I love the 6MT and if I lived in a place like Orange County or didn't have a brutal commute I would probably still have it. It was very rewarding (and at times terrifying) to be forced to pay attention all the time, to properly rev-match downshifts and deal with the hills here.

But that being said- the pdk is a joy and still makes for a very rewarding drive in the canyons. It does so much better in traffic I enjoy the car way more. My base carrera isn't as fast as the S but it's still very very fast and I feel more comfortable taking it closer to the limit than I ever did in the S.

The truth is, the 911 is a special car no matter what transmission is mated to it. For me, this is the best thing for where I am right now in my life. If I had one just for the weekends? Maybe I'd consider a manual again. But who wants to just drive a dream car on the weekends?!

Petza914

I find it interesting that this effects both 997.1 and 997.2 cars that have a completely different engine design - DFI vs non-DFI. Though I think the airbox design is similar. Mine doesn't do it but with a Fabspeed intake and supercharger, my induction setup is very much non-standard so not a good comparison. I have not really noticed it when driving my wife's car, but don't drive it very often.

RiccardoB

I have a 2011 C4S MT w/ 27Kmile and I noticed the same. Between 2500 and 3000 rev, the engine stumble just a little and then it goes away once you are above 3000. The stumble/hesitation is more marked if the engine is cold.
It could be something related to the exhaust/catalytic converter?

Fahrer

My 2008 has about 30K miles on it. I always noticed a slight flat spot in the power curve in the range folks are describing. It was much improved when I replaced the engine air filter.

Bruce In Philly

2009 C2S 135K miles

BIG UPDATE: I replaced the hydraulic valves, one on each bank, that triggers/controls the variocam system. Hail Mary pass.... I've wanted to try this for a long time. Did it work? NO! No difference. Wasted money again.

Part Number: 9A1-105-308-03
Part Name: Hydraulic Valve
Price: $135.49
Quantity: 2
Total: $270.98

Peace
Bruce in Philly

INTMD8

^ Not sure what kind of data list you can get on these with aftermarket software but on the cars I work on you can look at a few parameters which are commanded camshaft position, actual and error.

If actual is following commanded with no error than there is nothing to gain by addressing components in that system.

I feel this now and then in my car, also more prominent when cold/warm up. I suspect it could be fixed with access to the calibration but that is just a guess.

evo9

FWIW - I have same 'flat-spot / power-lull, etc' symptom on my 2010 C2S 6MT. Does not happen all the time, but very noticeable when it occurs. Nice to know I'm not alone... :-)

strickrn

Thanks for this explanation. My 2009 C2S MT has this little "shuffle" around 2,600 RPM. I've always wondered why the torque curve is so flat at this point....Duh, the engine management is switching modes and is normal...FINALLY. Thanks again.

Hindsight2010

Same thing on my 2009. I suspected right from taking ownership of the car that it was an engine management issue from the factory and likely did it since new. I just deal with it and consider it part of the car's character. It can be annoying but whatever. Just keep the car about 3500 RPM all the time and you'll never have to worry about it

Phrog Phlyer

Bruce Sorry to bring up a sore subject from the past but back in 2017 you posted a YouTube video espousing just to unhook the electrical connector and it would solve the problem. I deduce that since you are still posting about it that you either hooked the connector back up or it didn't solve your problem.
On another note, on the operation of the valve - When I start my car (cold start/first start of the day) the valve opens as the cold start idle increases and then slowly closes as the idle comes down. Then of course opens above 27-2800 RPM - Is that the way it is supposed to work?

Bruce In Philly

2009 C2S 157K miles

Well......... nothing is simple... especially when your mind plays trick on you.... er um... me.

So, in short, I still have the issue. Period.

Unhooking the vacuum valve located on the right side of the aribox, seems to have mitigated the effect of the drop out. Why? I don't know. Maybe it is just psychological due to what appears the valve changing over at the same time as the jerk... less stuff coming into your senses as there is no sound change. Or, maybe there is a bit of turbulence created in the intake as the valve flap moves?

But the fundamental reason for the hesitation appears to be the valves transitioning to high-lift..... no one knows for sure but this is the working assumption. Now I have to say, the problem has lessened over the last few years... but then I have the valve unhooked all this time.

Back when I got the car, at 26K miles, I took it to the dealer, the tech took a ride and he felt it... said something about no Porsche bulletins, he heard about this from others, and "keep an eye on it". Others who have it contacted me... one guy was so incensed he was threatening to sell the car. Under certain circumstances.... going up a rise, very slightly accelerating. bringing the RPMs up from low (ensuring the valves were in their low state).... well you could get a nice jerk. When I got the car, I kept thinking I ran over a stick or rock in the road.

I tried what I thought was everything.... the dealer, for free, reloaded the ECU firmware.. in the hopes Porsche modded the code in its later releases. I asked them to do this because my friend at Ford, who felt the issue, said it was most likely a software problem... he noted Ford will update the software without telling anyone so these problems "go away" with later-built units. After the update, I was like "CURED!" .... um no..... phsycho issue again. A week later my perceptions were back to normal.

I replaced those hydrolic valves on the side of the engine that re-routes oil flow for the valves.... nothing but wasted money.

There is only two more things that I can think of doing.... changing the plenum to get at that S-model flap back there, and there is another oil valve on the top of the engine. But..... I just live with it and as I noted, unplugging the air valve appears to mitigate the issue somewhat. BTW, that valve makes the induction noise go from higher-pitched to lower-pitched... oooo ahh..... but unhooking it give you the lower pitch all the time... not a bad thing.

One other oddity..... when the valve transition occurs, and car jerks, I can hear a "fssht" at the same time with the windows down and next to a wall. What is this oddity? I dunno.. related? Well yes in that a few things are going on when those valves transition.... vacuum leak? maybe..... One thing I was hoping for was that if something is breaking.... it would surface by now... it should have really broken by now.... but nope. It is... well...."an undisclosed feature" of the car.

So..... it is super simple to experiment by disconnecting the electrical line to that valve. Keep in mind, it will throw a code in the Durametric but not a dash light. Further, you may like the enhanced sound at low revs. According to Porsche published literature, this flap is for aesthetic purposes only... nothing to do with performance so it can't hurt anything. My super-duper imagination has concluded that when the flap moves, a bit of air turbulence is creating causing a slight drop in power.... but honestly, I have no idea... I just made that all up.

Regarding the flap's involvement during startup..... I doubt it has anything to do with starting up as Porsche said it is aesthetics only. Further, the valve is open or closed, no intermediate values. I think with the car off... the valve is open.... when you start the car, the vacuum closes the valve.... how fast? Depends on how fast the car can build vacuum in those lines. At 2.7K or thereabouts ... the computer triggers this stuff.... the solenoid valve closes and blows off pressure and the spring loaded plenum valve opens now no longer being held there by vacuum. I even changed out that valve thinking it maybe leaky.

Again, try disconnecting the electrical from back of the valve..... you won't hurt anything. See what happens to the sound... or 2.7K transition.

Peace
Bruce in Philly

How the valve works....